Microstructure and mechanical and thermal shock properties of hierarchically porous ceramics

Hierarchically porous Al2O3 ceramics with a porosity of 30–69% containing small intergranular pores and large pores created by a pore-forming agent were fabricated by gel-casting followed by partial sintering with starch addition. The influence of various pore types on the mechanical and thermal shock properties of the ceramics was subsequently investigated. A thermal shock parameter K was introduced to evaluate the dependence of strength degradation rate on the thermal shock temperature difference, and a new method for calculating the intergranular porosity and extrinsic porosity of the porous ceramics was developed. A low thermal shock strength degradation rate was obtained at a high ratio of fracture toughness (KIC) and elasticity modulus (E) of the material, which was achieved by decreasing the relative fraction of spheroidal extrinsic pores. However, the presence of these pores increased both the KIC and E values.